This application claims the priority of Korean Patent Application No. 2003-46125, filed on Jul. 8, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
An apparatus consistent with the present invention relates to a projection image display that enlarges and projects an image to be displayed and, more particularly, to a projection image display that projects image information at a variety of aspect ratios.
2. Description of the Related Art
Projection image displays are devices which modulate light emitted from an illumination unit using an optical modulator, such as a liquid crystal display panel and a digital micromirror device, to correspond to image information and enlarges and projects the image information onto a screen.
The projection image displays need to display image information having a variety of aspect ratios, such as common image information having an aspect ratio of 4:3, high definition (HD) image information having an aspect ratio of 16:9, and wide image information having an aspect ratio of 2.35:1. In general, an optical modulator has an aspect ratio of 4:3. In order to display image information having a variety of aspect ratios, a method of masking unused pixels of the optical modulator may be needed. FIGS. 1A–1C show examples in which common image information, HD image information and wide image information are displayed using an optical modulator 1 having an aspect ratio of 4:3. When the image information has an aspect ratio of 4:3, a total region T of the optical modulator 1 is used as an optical modulation region. When HD image information is displayed, only a region H, which is defined to have the aspect ratio of 16:9, is used as the optical modulation region. Similarly, when wide image information is displayed, only a region W, which is defined to have the aspect ratio of 2.35:1, is used as the optical modulation region. In the HD and wide image information cases, pixels in the unused portions of an optical modulation region are turned “off.” For example, in a transmission optical modulator, the pixels in the unused portion are turned “off” so that light does not pass though.
The conventional projection image displays project image information having a variety of aspect ratios using the above-described method. However, the above-described method is not preferable with respect to optical efficiency because the conventional illumination unit is designed to radiate illumination light on the total region T of the optical modulator 1 based on image information having an aspect ratio of 4:3. However, when HD image information is displayed, incident light on a region other than the region H is not used effectively and is wasted. Optical efficiency in this case is lower than the optical efficiency that may occur when image information having an aspect ratio of 4:3 is displayed. This lower optical efficiency also applies to a case where wide image information is displayed.